Known in the art is a method of submerged arc spot welding which is carried out by means of an apparatus described in the book "Studies on, and Production Experience of Welding", in Russian, Yu. M. Slesarev "Weld-Plug Welding in the Construction and Road Building Mechanical Engineering", Mashgiz Publishing House, 1955, pp. 75-76. The method comprises securing a consumable electrode fast with respect to a current carrying device firing a welding arc between the end face of the consumable electrode and the product surface. The consumable electrode is not fed into a fusion space thus formed: it is rather fused only by stretching the welding arc as the electrode is consumed to an amount equal to the breaking length of the welding arc. At the moment the welding arc is fired, the end face of the consumable electrode is moved away from the surface of a product, and the welding current decreases.
While the abovedescribed method is very simple in practical implementation, it is rather inefficient because of a low concentration of heat release at the weld spot, a longer welding cycle time, increased specific consumption of welding materials and electric energy, the major part of electric energy being spent for building-up an excessive reinforcement of the weld spot. The fusion capacity of the welding arc is very low, and quality of the resultant weld spots is poor. Therefore, this method is only suitable for welding non-vital thin-walled structures.
Known in the art is a method for welding using weld plugs (SU, A, 108233) wherein welding is carried out with an electrode having a coating and fixed during welding with respect to a current carrying device (electrode holder), the electrode being fused during gradual feed into the fusion space with a substantially constant value of welding current.
As compared with the abovedescribed method, this method has a wide field of application owing to the feeding of the consumable electrode into the fusion space at a rate equal to the fusion rate and allows welding of thicker joints to be carried out with holes of the upper part being melt-shut with the electrode metal.
At the same time, a low electrode feed rate, the presence of the electrode coating and a low density of current which can be permitted in the electrode with this welding technique cause a very low concentration of heat investment in the weld spot, low fusion capacity of the welding arc, long duration of welding cycle, increased consumption of welding materials and electric energy and poor quality of welded joints.
Known in the art is a method of electrical arc spot welding with a consumable electrode which is carried out by means of an arc spot welding device (cf. Studies on, and Production Experience of Welding, Yu. M. Slesarev, "Electric Weld Plug Welding in Construction and Road Building Mechanical Engineering, Mashgiz Publishing House, 1955, pp. 78-79), wherein the submerged welding technique is used. A consumable electrode is fixed with respect to a current carrying device, the electrode is positioned over the surface of a part being fused, a welding arc is fired between the end face of the consumable electrode and the part surface. The electrode is fused by gradually lowering the current carrying device with the electrode, with the welding current and arc length remaining practically unchanged. The end face of the consumable electrode remains over the surface of the part being welded during the whole welding period, at a distance therefrom substantially equal to the welding arc length, and the end face of the consumable electrode is moved away from the part surface at a still greater distance at the moment the welding is over when the welding arc is stretched. The molten metal of the electrode is transferred to the weld spot in the form of large-size drops. A weld spot (electric weld plug) which is thus formed has a large reinforcement and small working area of fusion.
Owing to a power-assisted feed of the consumable electrode to the fusion space and protection of the welding arc with flux this method features somewhat higher heat concentration at the weld spot and fusion capacity of the welding arc as compared to the abovedescribed methods.
However, as the consumable electrode in this method is fed to the fusion space slowly, at a rate equal to the rate of its fusion, the welding process occurs with an extended (longer) welding arc occurring over the surface of a part being fused. This results in a low concentration of heat investment to the weld spot, longer duration of welding cycle, increased consumption of welding materials and electric energy, the major part of energy being spent uselessly to achieve an excessive reinforcement of the weld spot; a weld spot cannot be produced without reinforcement, and welded joints are of a poor quality.